In recent years, higher integration and higher speed of the LSI (Large Scale Integrated circuit) are progressing. However, a strong restriction is imposed on the number of pins to be assigned to the power supply due to the limitation on the number of pins of the entire LSI. Thus, a great number of circuit blocks share the power supply wiring. As a result, lowering of power supply voltage and rising in ground potential may occur during the operation of the LSI. Furthermore, false operation of the LSI may occur in the worst case. Such so-called IR drop problem is becoming more serious with progress in higher integration and higher speed of the LSI.